Heat exchanger fin structure



April 23, 1957 c. s. SIMPELAAR HEAT EXCHANGER FIN STRUCTURE Filed Aug.20, 1955 L LAMINA/esuuyfzv MM f 505 m? WWA 1 7////////////// 6a, 6a 7@7a United Seres, Parent HEAT EXCHANGER STRUCTURE Clyde S. Simpelaar,Racine, Wis., assigner to Medine Manufacturing Company, Racine, Wis., acorporation of Wisconsin Application August 20, 1953, Serial No. 375,394

17 Claims. (Cl. 257-245) The invention relates generally to heatexchange structures and more particularly to a iin construction for usetherewith.

The present invention is of particular value in connection with higheiciency heat exchangers, as for example, where the nal temperature ofuid being acted upon, either cooled or heated, is within ninety-tive toninety-nine percent of the inlet temperature of the heating or coolingiiuid, and where the density of heat exchange surface is in theapproximate range of three hundred or more square feet per cubic foot ofvolume. Expressed in another way, the invention is of particular use inlexchangers wherein the accomplished temperature change in one fluiddivided by the difference in inlet temperatures of the two iiuidsexceeds .95.v In certain heat exchange applications, exchangers whichcannot meet these requirements are commercially impractical, as forexample, in low temperature oxygen plant exchangers wherein it isessentialV that the exchanger volume be at a minimum to reduce exteriorheat losses, and where the entire process is commercially. feasible onlyby virtue of the availability :of high, eiiiciency heatexchangers.

The advantage 'of utilizing interrupted heat transfer surfaces such asthin strips or pins has been heretofore recognized and considerable workhas`been done in connection with the utilization of socalled strip or`pin fins. However,l past research work has indicated that whilegenerally it is desirable to. reduce the width of the fin in thedirection of iiow, reduction in the width of the ns apparentlyapproached a limiting value .beyond which further reduction failed toproduce a corresponding improvement in eiciency. Experiments conductedalong the above linesV have appeared toy support such analysis as actualtests. of heat exchange surfaces disclosed a gain in etiiciency as theiin width was reduced down to what appeared to be a critical or limitingfactor, beyond which, additionalreduction failed to show a correspondingimprovement in eiciency. Normally n de. signs applicable toy strip orpin fins are of necessity repetitious. in pattern, wherein the fins arein line in the direction of flow with other fins, and it has heretoforebeen expressed that it would appear that all that was necessary withrespect to in-line surfaces was that they be separated a few thousandthsof an inch.

The present invention is directed to a means of utilizing iins of thestrip or pin type which may be constructed'in widths in the direction offlow of considerably less than those heretofore deemed practical toachieve extremely high eiliciency.

Another object of the invention is the production of heat exchange.sur-face having the desired high efficiency which is capable of beingcommercially produced with present product-ion techniques and availablematerials.

Many other objects and advantages of the construction herein shown anddescribed will be obvious to those skilledfin Ithe art from the`disclosures herein given.

To'fthis end my invention consists in the novel convn 2,789,797,PatentedV Apr. 23,

ice

struction, arrangement and combination of parts herein shown anddescribed, and more particularly pointed out in the claims.

in the drawings, wherein like reference characters indicate like orcorresponding parts: y Y

Fig. l is a diagrammatic figure illustrating the present theory inconnection with sharp edged iin surfaces;

Fig. 2 is a similar diagrammatic ligure illustrating applicants theoryas applied to iin surfaces having a leading edge of finite thickness;

Fig. 3 is a semi-diagrammatic ligure illustrating a cross section of alin of linite thickness and applicants theory with respect thereto;

Fig. 4 is a diagrammatic figure illustrating applicants theory withrespect to laminar layer carry-over between in-line fin surfaces;

Fig. 5 is a diagrammatic figure similar to Fig. 4 illusf trating theapplication of the present invention thereto;

Fig. 9 is a sectional figure similar to Fig. 6 illustrating a modifiedform of construction; and p Fig. 1 0 is an end elevational viewof a pairof the iin structures illustrated in Fig. 9. i

rThe boundary layer theory with respect to immersedu bodies, firstformulated by Prandtl, brieiiy is that the tluid surrounding a body maybe divided into two portions:

(l) a thin layer close to the surface of the body in which the velocitygradient is large enough to produce viscous forces of appreciablemagnitude; and

(2) the remaining portions of the fluid outside this boundary layer inwhich the viscous forces may bey neglected in comparison with theinertia forces, or in other words where the Reynolds number may beassumed to be infinitely large.

The characteristics of laminar flow and turbulent flow were demonstratedby Reynolds and the Reynolds number of course is a dimensionless terminvolving flow area, and the velocity, density and viscosity of the uid,which defines the limits of laminar and turbulent iiowf. It, in effect,thus involves the characteristics of the iiuid and the operatingconditions under which it is employed.

The present theory with respect to the boundary I ayer formed by theiiow of a iiuid over an immersed surface is generally illustrated inFig. 1, wherein a thin laminar sub-layer adjacent the surface of theobject such as'ft'he plate P extends along the area ofthe object. Thelaminar boundary layer is adjacent the leading edge ofthe plate and aturbulent boundary layer may be produced follow` ing a zone oftransition from laminar to turbulent con-v boundary layer, likewise,offers similar resistance but, of course, not to as great an extent asthe laminar layer and may be considered as having a transition or buierlayer interposed between it and the laminar Vsub-layer, offeringintermediate resistance. It is believed that the general theoryinvolving laminar layers and the Prandtl boundary is of suicientlygeneral knowledge inV the rheat transferA art that the above is suicientfor the purposes of the present application. It will bepappreciated,however, that as the lankiinar layer acts as an insulating medium if thet theoretical approximation of Fig. 1 is correct, a theoretical fin ofthe length a would have minimum resistance to heat ow and thus,theoretically, would be the most effective width, but its minutephysical proportions would substantially preclude its use in a practicalcommercial structure. Likewise in such case a theoretical fin of lengthb would have an average maximum resistance and thus would be the mostineffective width. Furthermore, as there is a transitionfrom the laminarlayer to a zone of turbulence or eddying, with proportionately greatereiciency, a tin having a length greater than b would have greaterintermediate values of resistance and thus efficiency.

It will be particularly noted that the above analysis involves theutilization ofa fin member wherein a leading edge thereof tapers to aline edge and therefore theoretically has no thickness, whereaspractical applications require a n having a thickness of finite order,which from a practical standpoint would approach, or probably be asgreat as the thickness of the laminar sub-layer. Obviously, where afinite thickness is involved a considerably different action may beproduced. Figure 2 illustrates a pos- `sible theoretical analysis withrespect to the boundary layers in connection with a tin of finitethickness, in which case it is believed that as a result of the finthickness,- strong eddying or turbulence would be produced adjacent theleading edge of the fin member, thus` delaying somewhat the formation ofthe laminar sub-layer as illustrated, and on such theoretical basis afin having the dimension a would have a minimum resistance and maximumefficiency. The eddying action adjacent the leading edge of the finprobably would also delay the formation of the laminar layer and mayeven eliminate the formation of such layer as indicatedv in Fig. 2, inwhich case the distance, equivalent to the distance b of Fig. l, wouldbe-for practical purposes eliminated, and the efficiency theoreticallywould continuously increase as the fin width is decreased.

v From the above theoretical discussion with respect to the laminarlayer it will be appreciated that in connection with `fins having afinite thickness, a fin having a width or dimension in thedirection offlow which is less than the dimension c illustrated in Fig. 2,theoretically, should have exceptionally satisfactory performance, andas a result of experimentation and tests it is believed that thedistance approximating dimension c, at normal llowing rates would beequal to approximately one-tenth of an inch to one-eighth of an inch,assuming a fin thickness oli-approximately three thousandths of an inchto .012 inch. In other words, on the basis of the above theoreticalanalysis it would appear that the heat transfercficiency of the finwould increase as the dimension of the fin in the direction of flow,heretofore referred to as the width, is successively decreased belowone-eighth'to onetenth of one inch.

A However, as previously mentioned, research on heat exchange surfaceshas indicated that the practical results apparently do not conform tothis theory, as corresponding reductions in the fin width haveapparently not achieved a corresponding increase in efficiency of theheat exchange structure. p

Strip fins have normally been formed from sheet material by severing thesheet material along spaced parallel lines equal to the fin width, withalternate portions between the lines of severance being offset out ofthe original plane of the sheet, thus-forming two seriesgof fins each ofwhich are connected at their ends to the sheet, the fins of each serieslying in a common plane with the trailing edges of a preceding linspaced from the leading edge of the next in-line tin by approximatelythe same distance `as the width of the respective fins. Consequently, asthe width of the fin is reduced the spacing between in-line fins iscorrespondingly reduced; Studies and considerations have apparently notevaluated the in-'line spacing as a factor to be considered inconnection with the Overall etliciency of the heat exchange structureand, as previously mentioned, the conclusions of some people in thisfield have been that such spacing is of relatively little importance andeven a few thousandths of an inch would be sufficient to achievesatisfactory results. However, I am of the belief that the in-linespacing of the fins is an important factor which must be considered andthat by properly spacing the in-line fins highly efficient resul-ts maybe obtained and the full advantages of the use of narrow ns more fullyvrealized. This theoretical conclusion has been supported by actual testson heat exchange structures constructed in accordance with the presentinvention and compared with tests on structures embodying prior conceptson the subject. For example, in one test a considerable increase inefficiency was obtained merely by removing certain in-line fins toincrease the spacing between the remaining in-line fins, the increaseshowing a gain of from six to fourteen percent.

Figs. 3, 4, and 5 roughly illustrate the concept involved in connectionwith the spacing of in-line fins. Fig. .3 generally illustrates theboundary layer flow of fluid along the fin surface which, for thepurposes of explanation may be compared with a generally sticky orviscous material which is frictionally retarded at the fin surface andthus has a tendency to build up into a low velocity mass which isincreasing in thickness toward the trailing edge of the fin. However, asillustrated in Fig. 4, it is believed that the flow following thetrailing edge would tend to revert into its original state prior toengagement with the first fin surface, so that the mass tends to taperoff as illustrated in Fig. 3, which will hereafter be termed theboundary layer carryover. If, however, before the same can be completelydissipated the next in-line fin is reached, the result is an additionalbuild-up of a relatively low velocity, high resistance mass, the latterprobably increasing in thickness over that formed on the first tin. Thisaction is continued with each succeeding in-line fin, and as aconsequence thereof the fins are in effect enveloped in a highresistance boundary layer or mass, resulting in a reduction in the heattransfer efficiency of the structure.

I am therefore of the belief that if the distance between the trailingedge of a precedingfin and the leading edge of the next followingin-line fin is suitably spaced as illustrated in Fig. 5, substantiallycomplete dissipation of the high resistance uid mass may be achievedbefore the following in-line fin is reached, eliminating a carryover andpossible additional build-up on such following fin and resulting insubstantially uniform heat transfer between the fluid and each fin ofthe exchanger structure. It is my conclusion that by properlycorrelating the spacing between in-line fins with the fin width, thewidth of the fins may be reduced to any desired practical value and atthe same time fully utilize the increase in efficiency resulting fromthe decrease in fin width, whereby an exchanger of high efliciency andlarge heat transfer surface area per cubic foot of volume may beproduced.

Figs. 6 to 10 illustrate typical fin structures employing the presentinvention, and while I'have shown n structures of the nested channeltype, these structures are merely by way of example and it is believedthat the present invention may be readily applied by those skilled inthe art`to other forms of fin structures, as for example, serpentinestructures and the like.

Referring to'Figs. 6 and 7; the reference numeral 1 indicates generallya channel shaped fin structure, two of which are illustrated in thedrawings, which are constructed to be positioned in nested relation witha sufficient number of channel members being employed to extend acrossthe uid pass in which they are assembled, the channels extendingparallel to the direction of flow through' the pass. Each channel member1 comprises a pair of side wallsor' portions 2, each of which are 0E-set outwardly as indicated'at 3. The walls 2 are connected adjacenttheir upper edgesl as viewed in Fig. 7

einen??? .s by @plurality ef strinans .,f 4b. esenti 4d In nnnnel a' sfbf the 1nv nithe. thielsnes's ef, material. aan ns the Inernber 1. isni .feiilike thickness, rangingv fr in approXimatelyv .003 lto, $01,?rinch, the metal employed rnbly 'beine Conner,y aluminum er otherSuitable maf ...nai having' satisfactory heat transfer eharnetefistes.fscleaily' illustrated in Fig. `7, the` offset 3 is substantially equaltol the thicknessI of the metal employed, wheres' lily, the distancebetween the inner faces of the offset portions lisr substantially equalto the outer dimension between the portions abovethe offset, Vso'thatthe channel rnmbers may be nested or interloc'lted as illustrated in E7. The strip tins 4 are formed byseveririg the metal al. nsf sna'eedraaliei lines which extend frein one side wallto the opposite sidewalland deforming orolsettingthe 'mateiial'interniediate the respectiveslits to form the tinfistt.

'the embodiment illustrated in Figs. 6 andl 7, the nist'srrip in aan atfae'nignest elevaron as viewed in rigs. e and' 7, ineen 4c at the nextelevation, the an 4b at the next elevation and the fin 4d at the lowestelevation. This staggered pattern then repeats itself, the nent fin 4gbeing positioned at the highest elevation and successively followed bytins 4b, 4c and 4a', so that all the tins 4a are aligned inthe directionof flow and in like manner all corresponding fins 4b, 4c, and 4d arerespectively in alignment. Thus in lthe embodiment 'illustratedI eachin-line fin is separated from the preceding or fol# lowingin-line 'iinby a distance equivalent to they width of threefin's, It will beappreciated that when `a relatively large number of channel members A1are nested together theresulting s tructurecontains a plurality ofseries of fins positioned in sequential arrangementl with respect to thedirection of flow. Thus the lirst row of fins 4a ex-v tending across thefluid pass transversely to the4 direction of ilowforms the first series,the f'ns`4b the second seriesr the fins lo thethird and thev fins 4dthe'fourth. As the pattern repeats` the second transversely exteridfugrowv ffins 4c form the fourth series and so on throughout the length ofthe channel member, s o that the structure may bec nsidnered asclomprisinga plurality of groups of series', th fins in cach seriesbeing similarly arranged and the respective series beingsimilarly'arranged in their respective; sronps- The transverse spacingbetween the planes of the tins 4a, 4b, 4c and 4d, corresponding to thespacing between the respective tins illustrated in Fig. '7, isisubstantially uniform andthe oliset 3 in the side walls is so positionedthat the fin 4a of the adjacent channel memberis spaced alike distancefrom the tins 4d of the first or upper channel member, so that all ofthe respective fins lie in parallel planes which are substantiallyuniformly spaced. Thespacing of in-,line fins and the transverse spacingbetweenA the respective planes above referred to are de t'ermincd inaccordance with the theoretical explanation heretofore set forth,whereby the spacing between in-line fins is greater than the so-calledboundary layer carryover-from the preceding in-line tins, and thetransverse spacing is greater than the combined thicknesses of theboundary layers of adjacent fins along any point in the direction offlow, so that each iin functions substantially independently of theother ins and without interference between the boundary layers andboundary layer carryover of the respective tins.

`In the bulk of applications of the present invention the iin spacingwill normally range from ten to sixteen per inch, such dimension takenfrom the center line distance between strips normal to the direction offlow. liikewise in the bull; of the` applications of theI presentinvention the transverse distance between the trailing edges 'andleading edges ef edie'eent fins ei' the distniiee betweenthe` planes ofrespective in-line fins will range frein'fnpnnexiineteir 015 te 04%. TheWidth of enen ind dis-'ei iinin'tiife difeetie ef. new Will` nerineliyrn' 'entretiens three y-seesnss. to; Qn,

et' anineit. and the distance from the: -trailinsetigeci ne nn' o. 'theieading'edgs @eine next. infuus nnwir. run from approximatelythree-sixteenths to three-quarters of an inch. As previously mentioned,normal iin'thiels'-l nesscorresponding to thethickness of the materialform; ing lthe channel member will range from approximately .003to.0l2"inch.` W it will, be appreciated that in forming the tinstructitres in. 'the manner illustrated in Fiss-''nd 7. from thin stok,and' offsetting the respective fins 4a, 4b, 4c and rv4d differentamounts, the transverse lengths of the fins bef tween the walls` 2 willvary, the tins 4a and 4d being slightly longer than the fins 4b and 4c.vIn this type of iinstructure the fins preferably may be formedinasuit.I able die or the like,t he fins being offset above e below acenter line` cf whiehnaybeconsidered as passe.v ing through thejuncture's of the respective 'fins with thek sidewalls 2. Thus lthe tins421 and V4al"m'ay. be equally'. offset above and below thecenter'line,and in like man,- ner the tins 4c and 4b may be respectively offsetequal distances above and below such center line. The metal forming thechannel members 1 usually'is of copper, aluminum or Vother comparativelysoft metal which is, capable of owing a sufficient amount to compensatefor they diiference in lengths of the respective fins. Thusy in formingthe fins, the metal comprising the ns 4a and 4d would owoutwardlypthereby effecting a stretching action and increasing theeffective lengthv of the fin to compensate for the dilerence in lengththereof. Likewise, some compressive action may be produced in the othertins, depending on the particular method of production employed. i

Fig. 8 illustrates diagrammatically a iin pattern gen-` erally `similarto that illustrated in'Fig. 6 involving a l clorresponding spacingbetween irl-liney surfaces of three times the width of the individualiin so that the fin pat, tern repeats in series of fours. ln the patternillustrated in Fig. 8 tins 6a extend parallel to thedirection of flow asdo the ns 6c, while the fins 6b and 6d are slightly tilted or twistedangularly with respect to the direction of flow to increase thetransverse distance between the. trailing edges of the ns of one seriesand the leading edges 'of the tins of the immediate following series. Asmall twist to the tins as illustrated serves to increase suchtransverse spacing without materially aiecting the eiiiciency of thestructure and thereby enables the transf verse center lines of the finsto be positioned closer than in the construction illustrated in Figs.6A4 and 7, whereby` a greater area of heat transfer surface per cubicfoot of heat exchanger volume may be obtained. The constructionillustrated in Fig. S also illustrates the use of a iin pattern whereineach successive fin is at a lower elevation than the preceding linbefore the pattern repeats itself, whereas Fig. 6 illustrates astaggered arrangement.

Fig. 9 illustrates the utilization of a lin pattern wherein the spacingbetween in-line fins is twice the iin width, whereby the pattern repeatsitself in groups. of three.

Referring to Figs. 9 and l0, this structure also is illustrated ina'chann'el type of iin structure similar to that illustrated in Figs. 6and 7, the channel member 1 have` ing side walls 2 provided with olsetportions 3 whereby the lower offset portions 5 of ythe side walls areadapted to receive a similar channel member nested therein. In thisconstruction the iins 7a of the first series are posi,-VA tionedparallel to the direction of ow similar to the construction` illustratedin Fig. 6, while the second and third iins 7b and 7c are angled insubstantially the same manner as the tins 6b and 6rd illustrated in Fig.8. Like' wise as in the case of the construction illustrated in Fig.8,'the tins 7a, 7b and 7c are' arranged in symmetrical Order 0n thechannel member with sneeessivetins nvins less elevation than thepreceding, iin of the'partieular pattern group. This ennstrnetien may befabricatedin..

substantially 'the saine manner es deseribed. inu Fiss.. v6. and 7, thens 7b approximately falling on the center;

Wiebke# lineconnecting thel junctures of the tins at the oppositeslightly or may have the metal thereof slightly cornv pressed, while themetal forming the fins 7a and 7c ows or is slightlyl stretched` toaccommodate the difference in lengths.

Fig. ll illustrates one application of the present invention to a heatexchange structure illustrated in the present instance as including apair of Huid passes 8 formed by outer plates 9 and an intermediateseparated plate 10, the side edges of the passes being bounded by sidewall members 11, the channel members of each respective pass beingnested together to form in effect a fin slab withthe respective elementsbeing suitably bonded together to form a unitary structure. Suitablemeans may be provided at the respective ends of the structure forproviding inlet and outlet means for the fluids into their respectiveuid passes. This construction is similar to that illustrated in my priorPatent No. 2,606,007 issued August 5, 1952.

It will be appreciated that the present invention is adapted for use inany heat transfer structure utilizing strip tins, pin fins and the like,irrespective of the particular physical construction of the uid passes,etc., and could readily be employed in structures where the entire heattransfer tin surface is constructed from a single sheet of materialwhich is of corrugated or serpentine shape and from which the individualfins are struck up or otherwise formed.

It will be appreciated from the above description that I have provided anovel heat transfer structure and method of arranging the fins thereofto achieve maximum efliciency together with a high heat transfer surfacearea per cubic foot of heat exchanger volume and which permits theutilization of narrow fins of high eciency without interference betweenin-line iin surfaces.

It might be mentioned that where I have referred to the boundary layer,this term is intended to mean the layer ofrelatively low velocity Huidadjacent the fin surface, a carryover of which from one iin to anotherwill produce a material decrease in heat transfer ethciency.

Having thus described my invention, it is obvious that variousimmaterial modicationsmay be made in the same without departing from thespirit of my invention; hence, I do not wish to be understood aslimiting myself to the exact form, construction, arrangement andcombination of parts herein shown and described, or uses mentioned.

What I claim as new and desire to secure by Letters Patent is:

l. In av uid pass for heat exchangers, the combination of an elongatedrelatively thin uid pass structure, and a plurality of elongated striptins having their ends operatively connected to the opposite sides ofthe uid pass structure in heat transfer relation therewith, thethickness of the respective fins being less than the width thereof inthe direction of uid flow through the pass structure, said ns being ofsubstantially uniform width and arranged in a plurality of series, eachof which extends across the fluid pass transversely to the direction ofiiow therethrough, and to the individual fins, said series beingpositioned in repeated sequential arrangement with respect to suchdirection of flow, the fins of each seriesbcing positioned out of linein relation to the direction of flow with respect to the iins of thenext followingseries, the spacing transverse to the direction of flowbetween the trailing edges of the ns of one series and the leading edgesof the next series adjacent thereto being approximately from three to vetimes the thickness of said fins, and the spacing in the direction of owbetweenanyfins of corresponding series in line in suchdiflov'vdirection.`

2. In `a fiuid pass for heat exchangers, the eombina-1 tion of anelongated relatively' thin fluid pass structure; and a plurality ofrelatively narrow tins'having their ends operatively connected to theopposite sides of the iiuid pass structure in heat transfer relationtherewith,l the respective fins extending transversely in thinlongitudinal direction with respect to the direction of fluid iiowthrough the pass structure, said fins being arranged in a plurality ofseries, each of which extends across the fluid pass transversely to thedirection of iiow therethrough, and to the individual tins, said seriesbeing positioned in repeating sequential arrangement with respect tosuch direction of flow, the tins of each series being positioned out ofline in relation to the direction of ilow with respect to the tins ofthe next following series, the spacing transverse to the direction of owbetween the fins of one series and the ns of series adjacent theretobeing greater than the thickness of the boundary layers along said tins,and the spacing in the direction of flow between any ns of differentseries which arc in line in such direction being greater than the iinwidth and the boundary layer carryover in the flow direction from theadjacent preceding in line tin, under the particular operationconditions and uid characteristics involved.

3. A fin structure for heat exchange uid passes comprising a sheet ofthin metal of a thickness of approximately .003 to .012" formed toprovide a pair of body portions connected by an intermediate portion,the body portions providing means for securing the fin structure toopposite side walls of a heat exchange uid pass, the. intermediateportion of said fin structure being cut along parallel lines uniformlyspaced in the direction of tlow to form a plurality of individualsubstantially at strip iins which extend transversely between the twobody portions and have their ends operatively connected to therespective body portions, the width of said ns in the direction of flowbeing substantially uniform and from approximately /g" to M4, the finstructure being adapted to be positioned in a iiuid pass with suchintermediate portion extending in the same direction as the fluid flowthrough such a pass, each of said strip fins being laterally offset withrespect to the adjacent strip tins, said strip fins being offset in apredetermined pattern and sequence which repeats itself whereby eachstrip iin is substantially aligned in the direction of ilow with otherstrip ns, the pattern being such that the strip tins substantially inline are spaced apart in the direction of flow a distance offromapproximately to the offset distance between trailing and leading edgesof adjacent strip fins being from approximately .015 to .040", withalternate tins being positioned in planes extending substantiallyparallel to the direction of flow and intermediate fins being positionedin parallel planes extending angularly with respect to the direction ofliow.

4. A tin structure for heat exchange fluid passes comprising a sheet ofthin4 metal of a thickness of approximately .003" to .012" formed toprovide a pair of body portions connected to an intermediate portion,the body portions providing means for securing the tin structure toopposite side walls of a heat exchange fluid pass, the intermediateportion of said tin structure being cut along parallel lines uniformlyspaced in the direction of ow to form a plurality of individualsubstantially flat strip fins which extend transversely between the twobody portions and have their ends operatively connected to therespective body portions, the width of said iins in the direction ofiiow being substantially uniform and from approximately g" to 1A", the nstructure being adapt-l ed to be positioned in a lluid pass with suchintermediate portion extending in the same direction as the uid owthrough such a pass, each of said strip fins being laterallyl os'et`with respect to the adjacent strip tins, saidstrip.' tins being offsetin a predetermined patternandsequencet. which repeats itself wherebyeach strip iin is substantiaily laligned in tbe, dir-editen et tisnuwith4:aber @tric hns, tbe, pattern beingJ auch that the.; Siria nssubstantially in lineare erased apart in the direction of new? distanceof from approximately da", to 1%", the, oiset distance between trailingand leading edges of adjacent strip iins being from approximately .015,"Ato .040, with certain corresponding fins extending substantiallyparallel to the direction of flow andl other corresponding fins eX-tending angularly to the direction of flow.

l A yn structure for heat exchange fluid passes comprising a sheet ofthin` metal of a thickness of approximately .003 to. .'012` formed to.provide a pair of body portions connected to an intermediate portion,the body portions providing means for securing the lin structure; to,opposite side walls of ar heat, exchange fluid pass, the interrnefdiate`portion of said structure being cut along parallel lines uniformlyspaced in the direction of ow to form a plurality of individualsubstantiallyl at strip fins which extend transversely between the twobody portions and have their endsl operatively connected to therespective body portions, the width of said fins in the` direction ofowbeing substantiallyv uniform and from approximately :'ggf to 1/t thelin structure being adapted to be positioned in a uid pass with suchintermediate portion extending in the same direction as the iuidr owthrough suchl pass, each of said strip tins being laterally oiset withrespect to the. adjacent strip tins, said strip tins being offset in apredetermined pattern and sequence which repeats itself' whereby eachStrip iin is substantially aligned in. the direction et now with otherstrip fins, the pattern beingl such, that the strip ns substantially inline are spaced apart in the direction of llow a distance of fromVapproximately die to 2A, the` offset distance between trailing andleading edges of adiaeent strip` tine. beine ,from approximately .015 te.040, with each fin oi the structure being similarly positioned withreSpect to the third n therefrom in the 'direction of HOW'.

6 A iin structure for heat exchange fluid passes comprising a sheet ofmetal formed to provide a pair of body portions connected by anintermediate portion, the body portions providing means for securing theiin structure to opposite side walls of a heat exchange uid pass, theintermediate portion of said n structure being cut to form Plurdliiy Q.individual tinsI which extend transversely between the two body portionsand have their ends operatively Connected to the respective bodyportions, the lin structure being adapted to be positioned in a iluidpass with such intermediate` portion 'extending generally in the samedirection as the fluid flow through such a pass, each of said tins beinglaterally offset with respect to the adjacent fins, said lins'beingolset in a predetermined pattern and sequence which repeatsitselfwhereby each n issubstantally aligned in-'the direction of flowwith other ns, the patternbeing such that the tins substantiallyin lineare spaced apart in the direction of ow a distance at least twice thewidth of the hns in such direction, the offset distance between adjacentns being greater than the corresponding dimensions of the boundarylayers along said tins, andthe distance between in-line ns being g1; Vr.than they boundary carryover from aprecedin'g ii; t. the direction ofow, under the particular operating'conditions and fluid characteristicsinvolved in the particular Huid pass, with alternate fins beingpositioned in planes extending sub- Stantiauy Parallel to the directionof ow andiintermediate ins being positioned in parallel planes extendingangularly with respect to the direction of llow.

7. A lin structure for heat exchange fluid passes comprising a sheet ofmetal formed to provide a pair of body portions connected by anintermediate portion, the body portions providing means for securing then structure to opposite side walls of a heat exchange uid pass, theintermediate portion of said iin structure being cut to fer-1nA a.plurality et individual tins which extend; tiene# rersftly between the.two, body portions` and; have; their endsy operatively connected to therespective body-y ptn?-AA tibns, the iinv Structure being adapted to benositpned in a duid pass with such intermediate portion 'exten generallyin the same direction as the fluid flow th ugh, s uch a pass, each ofsaidr fins being laterally offse respect to the adjacent fins, saidfins, being ois'et predetermined pattern and sequence which repeatsitselwhereby each iin is substantially aligned inA the direction` of flowwith other fins, the pattern being such` that he, ns substantially inline are spaced apart in the dire t tion of flow a distance at leasttwice the width of lins in such direction, the olset distance betweenVaid. jacent tins being greater than the corresponding dim l, sions ofthe boundary layers along said tins, and the; di tance between in-linens being greater than the behind?1 ary carryover from a preceding fin inthe dirrectionv g flow, under the particular operating conditions andilu characteristics involved in the particular iiuid pass, certaincorresponding ns extending substantially par allel to the direction offlow and other corresponding ns extending angularly to the direction ofdow.

V3,. A iin structure for heat exchange fluid passes com;

, prising a sheet of metal formed to provide a pair of body;

portions connected by an intermediate portion, the body portionsproviding means for securing the strntrire to opposite side walls of aheat exchange fluid pass, the, intermediate portion of said finstructure being cut to form a plurality of individual tins which extendtransversely between the two body portions and have their endsoperatively connected to the respective bodyI por tions, the iinstructure being adapted to be positioned in,` a ilni'd pass with suchintermediateV POltrion extending` generally in the same direction es.the, duid. flew thrnusby such a pass; each of said tins being laterally'offset withl respect 'to the adjacent dus, Said tins, being Offset in apredetermined pattern and sequence which repeats itselfk whereby eachllin is substantially aligned in the direction of iow with other ns, thepattern being such that the. fins substantially in line are spaced apartin the direc-1, tion of flow a distance at least twice the width of 'thefins in such direction, the offset distance between adjaf cent` tinsbeing greater than the corresponding dimenf sions of the boundary layersalong said tins, and vthe, distance between ineline iins being greaterthan the bound-V ary carryover from a preceding iin in 'the direction ofllow, onder the particular operating conditions and'lluidcharacteristics involved in the particular uid pass,k with each tin ofthe structure being similarly positioned with respect to the third tintherefrom in the direction of flow.

9 In a huid pass for heat exchangers, the combina? tion of an elongatedrelatively thin fluid pass structure, of a plurality of relativelynarrow tins each, having at least one end thereof operatively connectedto the Huid; pass strnctnre in heat transfer relation therewith, therespective fins extending transversely in their longitudi-h naidirection with respect to the direction of iluid flow through the passstructure, said ns being arranged in a plurality of series, efachofwhichextends acrossthe iluid pass transversely to the direction of flowtherethrough, and to the indiyidual tins, said series being positionedin repeating sequential arrangement with respect to such direction ofhow, the ns of each yseries being positioned out of line in relation tothe direction of iiow with re-v spent to the fins of the next followingseries, the Spacing transverse t0 tbe direction. of 110W between thefins of one series and the ns of series adjacent thereto being greaterthan the thickness of the boundary layers along said iins, and thespacing in the direction of ow between any fins of different serieswhich are in line in such direction being greater than the n width andthe boundary layer carryover in the ow direction from the adjacentpreceding in line fin, under the particular operation conditions andfluid characteristics involved.

11 v'.' In a fluid pass for heat exchangers, the combinationv of anelongated relatively thin fluid pass structure, of a plurality ofrelatively narrow fins having their ends operatively connected to theopposite sides of the fluid pass structure in heat transfer relationtherewith, the respective fins extending in their longitudinal directiontransversely with respect to the direction of fluid ow through the passstructure, said hns being arranged in a plurality of series, each ofwhich extends across the fluid pass transversely to the direction offlow therethrough, and to the individual fins, said series beingpositioned in groups sequentially arranged with respect to suchdirection of flow, corresponding series of the respective groups beingsimilarly arranged and the fins of each series of a group beingpositioned out of line in the direction of ow relative to the ns of theother series of such group and in line with respect to the fins of thecorresponding series of the next following group, the spacing transverseto the direction of owv between the trailing edges of fins of eachseries and leading edges of fins of the following adjacent series beinggreater than the thickness of the boundary layers along said fins, andthe spacing in the direction of ow between consecutive in line fins ofcorresponding series of adjacent groups being greater than the fin widthand the boundary layer carryover in the flow direction from the adjacentpreceding in line fin, under the particular operation conditions andfluid characteristics involved.

11. A fin structure for heat exchange fluid passes cornprising a sheetof thin metal formed to provide a pair of body portions connected by anintermediate portion, the body portions providing means for securing thefin structure to opposite side walls of a heat exchange fluid pass, theintermediate portion of said fin structure being cut along parallellines spaced in the direction of flow to form a plurality of individualsubstantially at strip fins which extend transversely between the twobody portions and have their ends operatively connected to therespective body portions, the fin structure being adapted to bepositioned in a fluid pass with such intermediate portion extendinggenerally in the same direction as the fluid flow` through such a pass,each of said strip fins being laterally offset with respect to theadjacent strip fins, said strip fins being offset in a predeterminedpattern and sequence which repeats itself whereby each strip fin issubstantially aligned in the direction of flow with other strip fins,the pattern being such that the strip fins substantially in line arespaced apart in the direction of flow a distance at least twice thewidth of the strip fins in such direction, the offset distance betweenadjacent strip fins, transverse to the direction of flow being greaterthan the corresponding dimensions of the boundary layers along saidfins, and the distance between immediately adjacent in-line fins being-greater than the boundary layer vcarryover from a preceding fin in thedirection of ow under the particular operating conditions and fluidcharacteristics involved in the particular fiuid pass.

12. A fin structure for heat exchange fluid passes comprising a sheet ofthin metal of a thickness of approximately .003 to .012 formed toprovide a pair of body portions connected by an intermediate portion,the body portions providing means for securing the fin structure toopposite side walls of a heat exchange fluid pass, the intermediateportion of said fin structure being cut along parallel lines uniformlyspaced in the direction of flow to` form a plurality of individualsubstantially flat strip ns which extend transversely between the twobody portions and have their ends operatively connected to therespective body portions, the width of said fins in the direction offlow beingA substantially uniform and from approximately g to Mz", the nstructure being adapted to be positioned in a fluid pass with suchintermediate portion extending in the same direction as the fluid flowthrough such a pass, each of said strip fins being laterally offset withrespect to the adjacent strip fins, said strip fins being offset in apredetermined pattern and sequence which repeats itself whereby eachstrip fin is substantially aligned in the direction of flow with otherstrip fins, the pattern being such that immediately adjacent strip finssubstantially in line are spaced apart in the direction of ow a distanceof from approximately 3A6" to the offset distance between trailing andleading edges of adjacent strip fins being from approximately .015" to.040".

13. A fin structure as defined in claim l2 wherein the fins arepositioned in planes extending substantially par allel to the directionof flow.

14. A fin structure as defined in claim 12 wherein each fin of thestructure is similarly positioned with respect to the fourth fintherefrom in the direction of flow.

15. A fin structure for heat exchange uid passes comprising a sheet ofmetal formed to provide a pair of body portions connected by anintermediate portion, the body portions providing means for securingAthe fin structure to opposite side walls of a heat exchange fluid pass,the intermediate portion of said fin structure being cut to form aplurality of individual fins which extend transversely between the twobody portions and have their ends operatively connected to therespective body portions, the fin structure being adapted to bepositioned in a fluid pass with such intermediate portion extendinggenerally in the same direction as the fluid flow through suchA a pass,each of said ns being laterally offset with respect to the adjacentfins, said fins being offset in a predetermined pattern and sequencewhich repeats itself whereby each fin is substantially aligned in thedirection of flow with other fins, the pattern being such that the finssubstantially inline are spaced apart in the direction of flow adistance at least twice the width of the fins in such direction, theoffset distance between adjacent fins being greater than thecorresponding dimensions of the boundary layers along said fins, and thedistance between immediately adjacent in-line fins being greater thanthe boundary carryover from the immediately preceding fin inthe'direction of flow, under the particular operating conditions andfluid characteristics involved in the particular uid pass.

16. A fin structure as defined in claim 15 wherein the fins arepositioned in planes extending substantially parallel to the directionof ow.

17. Afin structure as defined in claim 15 whereineach n of the structureis similarly positioned with respect to the fourth fin therefrom in thedirection of ow.

References Cited in the file of this patent UNITED STATES PATENTS2,360,123 Gerstung etal Oct. 10, 1944 2,549,466 Hoheisel Apr. 17, 19512,606,007 Simpelaar Aug. 5, 1952 FOREIGN PATENTS 915,093y France July 8,1946 1,018,691 France. Oct. l5, 1952

